Synchronizing arrangement for a regenerative telegraphic repeater utilizing signal transitions



March 7, 1961 SYNCHRONIZING ARRANGEME Filed Nov. 26, 1954 P G. WRIGHT ETAL 2' Sheets-Sheet 1 1106 1026 M s -P 2 O O O TO GATES mom 1150 TO 110105 ANDflC'HO 13F u 1 L. 3

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1105o,1107o,11090, 1 110110 m 110130 M S INVENTORS. E. R6. WRIGHT v. J. TERRY BY AGENT March 1961 E. P. G. WRIGHT EI'AL 2,974,197

SYNCHRONIZING ARRANGEMENT FOR A REGENERATIVE TELEGRAPHIC REPEATER UTILIZING SIGNAL TRANSITIONS Filed Nov. 26, 1954 2 Sheets-Sheet 2 22F TO 11010, 11030, 11050} TO 1100, 1102011040} L 11060, 11C80,11C12O lNVEN'I "ORS. E. P. 0. WRIGHT 2 BY V. J. TERRY Qua/$0M AGENT United States Patent SYNCHRONIZING ARRANGEMENT FOR A RE- GENERATIVE TELEGRAPHIC REPEATER UTI- LIZING SIGNAL TRANSITIONS Esmond Philip Goodwin Wright and Victor John Terry, London, England, assignors to International Standard Electric Corporation, New York, N.Y.

Filed Nov. 26, 1954, Ser. No. 471,422

Claims priority, application Great Britain Dec. 10, 1953 5 Claims. (Cl. 178-70) This invention relates to electric communication channels conveying intelligence in the form of a code and is an improvement in or modifications of the invention described in US. Patent 2,749,386, issued June 5, 1956, hereinafter referred to as the parent specification.

In the last mentioned specification there is described an electronic regenerative repeater for start-stop printing telegraph signals sent at regular intervals, comprising a non-continuously running time base for timing the regeneration operation and means for starting the time base at different positions in accordance with differences in time of arrival of a start element. Such an arrangement was possible because the time of arrival of a start element could, with continuously received signals, be predicted within certain limits of time.

With start-stop signal combinations the time occupied by the start and stop elements is wasted as regards conveying intelligence and it is therefore common to send telegraph signals over radio channels by synchronised systems, that is, systems in which the time scale circuits at transmitter and receiver are continuously running and are kept in synchronism by separate synchronising signals. It is a very simple technical matter to arrange synchronous operation by means of a separate signalling channel but such an arrangement is not economical, particularly on long radio channels.

It is the object of the present invention to provide a simple means of control of synchronism by the signals themselves.

It will be appreciated that in all but one of the 31 combinations of the International Telegraph Alphabet No. 3 there is at least one transition between the two signalling condiitons (the exception being the letter shift combination) and that any such transition may be expected at only certain of the times on such time scale. The present invention is therefore an extension of the principle of the invention of US. Patent 2,749,386 to continuously running time scales and makes use of the times of arrival of transitions between the two signalling conditions representing intelligence bearing signal combinations instead of merely the transitions from mark to space representing the beginning of a start element in start stop signals.

The invention will be described as applied to the system described and claimed in British Patent 771,301, May 1, 1957. In that system check elements for checking the accuracy of the elements of a signal combination are transmitted in addition to the signal elements and the system is such that signal combinations received from a teleprinter are re-transmitted over a synchronous channel and therefore without start and stop elements. The combinations transmitted over the synchronous channel are seven element combinations made up by adding to the intelligence carrying elements of each combination received from the teleprinter two check elements. These check elements are added at the end of the other combinations.

Whilst no signals are being transmitted over the synchronous channel the normal condition of such channel in an ordinary synchronous system is marking, in the system using the above mentioned check elements the first five elements in each cycle of the time scale are treated as if they were elements of a signal combination and check elements are added. As described in the above mentioned British Patent 771,301, during a condition of the channel preparatory to sending signal combinations but when no intelligence is being transmitted, seven unit combinations MMMMMSS will be transmitted. The arrival of the mark to space transition can then be used to start the time scale in a position corresponding to the time of the transition in a full cycle. Thereafter the time scale runs continuously but is corrected for lack of synchronism as will be explained.

This embodiment of the invention is illustrated in the accompanying drawings which are block schematic diagrams which are functional in nature and in that respect are similar to those of the above-mentioned British patent. References are therein given to other specifications from which full particulars of the circuits represented by the functional symbols used may be obtained, but these functional symbols are now so largely used that they are familiar to those skilled in the art, by whom the corresponding ful-l circuits can readily be constructed.

In these drawings:

Fig. 1 shows the time scale circuit, and the circuits for starting, stopping and correcting the positions of said time scale.

Fig. 2 shows a circuit for determining what corrections are to be applied to keep the time scale in synchronism with that at a transmitter.

These drawings are functional diagrams each symbol used standing for a device performing a particular function, the physical nature of the device and its manner of performing the function being well known. The reference characters for the various symbols have been allotted in such a manner as to denote the nature of the device and also the figure of the drawings upon which each appears. Thus each reference character consists of a numeral followed by a letter. Thus counting circuits are denoted by the letter C and the various counting circuits are distinguished by the preceding numeral. The first digit of the numeral indicates the figure upon which the symbol denoted by the reference character appears.

Gate circuits are denoted by the letter G; gate circuits 101G to 114G appear on Fig. 1 and gate circuits 201G to 2146 on Fig. 2. Multi position switches are denoted by the letter F, the difierent positions of these switches being denoted by rectangles within which diiferent numerals or letters appear. In the case of two position switches the letters denoting the positions have some relation to the functions performed by the switches in the respective positions.

The devices shown are all to be considered as made up of static electric switches. Thus, a two position switch such as 11F, with positions ST and SP can take the form of two cold cathode gas filled tubes interconnected so that when one is made conducting the other becomes non-conducting. When one of the tubes is conducting it supplies a potential to an output conductor. This output conductor is shown as a line adjacent only to the device or devices to which such potential is applied and the reference character applied to the line is the same reference character as the position which gives the potential output but with the letters in the lower case. Thus, an output from the tube ST of 11F is denoted 11 st. Similarly the different counter circuits can give an output from their various positions which output is similarly denoted by the same reference character as the counter (but with the letter in the lower case) followed by the number of the counter position. Thus, a conductor 3 on which counter 12C gives an output in position 2 is denoted 12c.2.

11C denotes a counting circuit which may take the form of that shown and described in U.S. Patent 2,787,657, issued April 2, 1957 and may control the application of potentials to various other circuits at various times in the time scale of counting. This counting circuit counts pulses from a source of pulses. Negative pulses from this source appearing on the lead marked P are applied, as will be explained later, to the counting circuit and cause successive elements of a chain of static electric switches (in the example referred to cold cathode electric discharge gaps) to be placed in conducting condition.

The pulses recur at a frequency of 500 kc./s. and thus successive elements are made conducting at intervals of 0.2 millisecond. The cycle of the counting circuit is 145 milliseconds. Only certain elements in the counting circuit are indicated, viz. those operated at times 0, 98, 102 and 144.8 milliseconds from the time of the pulse that operates the first element 0.

Assuming a speed of transmission such that each signal element occupies 20 milliseconds, the first five elements of a recived signal combination occupy 100 milliseconds and when transmission first commences a signal combination of five marks followed by two spaces is received as explained above. The transition from mark to space therefore occurs nominally at 100 milliseconds in a time scale of which Zero represents the commencement of the first signal element. The counting circuit is therefore set to commence initially in the neighborhood of 100 milliseconds in its time scale. The drawing shows conditions for setting it at this time at 102 milliseconds.

The incoming signals received over the radio channel are detected and applied to a demodulator which causes pulses from the same source as that supplying -P to appear on one or other of two conductors marked M and S respectively in Figs. 1 and 2 according as the incoming signal condition is mark or space, as described in US. Patent 2,787,657. Conductor S provides one input to a gate 101G, another input being provided by the element 1 of a two position switch 12F. Switch 12F is normally in the position in which element 1 thereof is conducting.

When therefore the incoming signal condition changes to spacing, gate 101G is opened (it requires two input conditions to open it as denoted by the numeral 2 inside the circle) and presents one input condition to gate 105G which also requires two input conditions to open it. The other condition is supplied by switch 11F in its normal condition of element SP conducting. Gate 105G is therefore opened and element ST of switch 11F made conducting, element SP becoming non-conducting. The switch 11F provides a momentary pulse on the lead marked 11 whenever it changes over from one condition to the other. This pulse is applied over gate 102G to set (or reset) counter 11C in position 102 milliseconds from zero of the time scale, the switch 23F being in position 4 and supplying a second input gate 102G. The switch 23F is normally reset to position 4 as will be clear from a later part of the description.

Since element ST of switch 11F is now conducting a gate 103G opens at each pulse from --P and the counting circuit 11C is stepped by these pulses.

The counting circuit 11C applies potentials to one input to a gate 104G at 105 milliseconds, i.e. 3 milliseconds after starting up, and at five milliseconds thereafter up to zero in the time scale. Another input is supplied by a switch 12F when in its normal position 1 and a third input by the mark conductor 1N1. Each time a marking condition is found, therefore, gate 104G is opened and passes forward a condition to open gate 11GG and give a step to counter 12C. Counter 12C has three positions so that marking conditions found at two consecutive times of examination drive this counter to position 2. In this position gate 108G is opened, followed by the opening of gate 107G and the restoration of switch 11F to position SP. The application of pulses to the time scale ceases, as gate 103G is no longer opened, and the momentary pulse on 11ft advances the counting circuit 11C to position 102 and resets counter 12C to position 0.

It will be appreciated that in the case of a true start the spacing condition should persist for 45 milliseconds (the last element being assumed to last for 25 milliseconds) as described in the said British Patent No. 771,301. The channel may be subject to interference which will cause a marking condition to appear during this 45 milliseconds and a true start may be rejected because of this interference. There will however be repetitions of the starting sequence and the counting circuit 11C will be set in operation on one of these repetitions. In fact seven such repetitions will occur per second and if the start cannot be made effective the channel is unlikely to be fit for transmission.

The arrangements described, however, ensure that a fading condition giving a spurious start condition does not result in continuous running of the time scale circuits.

The counter 11C which provides a time scale for controlling the operations of the receiver and regenerator is stepped by a source of pulses of the same frequency as that stepping a similar counting circuit which provides a time scale for controlling the operations at the transmitting end of the channel. During reception there is a possibility of synchronism being lost if there is any difference in the stepping speed of these two time scale circuits. The invention provides a correcting device which corrects the movement of the time scale at the receiver to compensate for any apparent loss of synchronism in a manner which is similar to that used in the said US. Patent 2,749,386 for correcting for early or late arrival of a start element in start-stop reception.

The mark and space leads M and S from the demodulator above referred to are connected to the respective elements M and S of a two position switch 21F, so that during a marking condition element M is operated, during a spacing condition element S is operated. At each change-over a pulse is produced on conductor 21ft.

A second two-position switch 22F is placed in position E by potentials applied from the counting circuit 11C at 10, 30, 50, 70, 110 and 130 milliseconds from zero on the time scale and placed in position L by potentials applied from the counting circuit 11C at times corresponding to normal transition times viz 0, 20, 40, 60, and 120 milliseconds (the time of milliseconds is omitted for reasons which will appear later).

If a transition between marking and spacing conditions which should occur at e.g. 20 milliseconds in the time scale, occurs later, i.e. between 20 and 30 milliseconds, the transition is late and when a pulse occurs on 21ft due to the transition, switch 22F is in position L. If on the other hand the transition which should occur at e.g. 200 milliseconds occurs before that time i.e. between 10 and 20 milliseconds, the transition is early and a pulse occurs on 21ft when switch 22F is in position E.

A multi-position switch 23F is reset into its middle position 4 by output 11c from counting circuit each time the scale reaches 105. It will be seen that switch 22F in position E denotes an early transition and in position L a late transition. This is used to drive switch 23F towards a higher position for each late transition and towards a lower position for each early transition.

With switch 23F in position 4 and switch 22F in position L, potentials are applied from 23 4 and 22f1 to a gate 201G which is opened to apply an input to a gate 202G. If now in this condition a signal transition occurs, a pulse applied over 21 to gate 202G passes through the gate and operates switch 23F to position 5.

With switch 23F in position 5 and switch 22F in position L, a gate 2036 is opened and applies an input to 5 gate 204G. It now a pulse is applied over 21ft it passes through gate 2046 to drive switch 23F to position 6.

With a pulse occurring on 21ft when switch 23F is in position 6 and 22F in position L, gate 205G is opened to drive switch 23F into position 7.

Thus three late transitions in succession after 105 milliseconds in a cycle of the time scale and during the earlier part of the next cycle of the time scale will drive switch 23F into position 7.

Three early transitions in succession will on the other hand, drive switch 23F into position 1.

With switch 23F in position 4 and switch 22F in position E gate 206G is opened and an input applied to gate 207G and a pulse on 21ft passes through this gate to drive the switch 23F to position 3.

With switch 23F in position 3 and 22F in position E gate 208G is opened and applies an input to gate 209G. When a pulse occurs on 21ft it passes through gate 209G and drives switch 23F to position 2.

With 23F in position 2 and 22F in position E a pulse on 21ft passes through gate 2106 to drive switch 23F into position 1.

If the switch 23F has been driven in one direction or the other by late or early transitions and a transition of the other kind occurs, it is driven in the reverse direction. This is subject to the exception that it is not driven into position 4 from either position 3 or back from position 5, though similar gating arrangements could be applied to do this if thought necessary.

If, however, switch 23F has been driven into position 2 by two successive early transitions it is driven to position 3 it the next transition is late. This is done by opening of gate 2116 when switch 23F is in position 2 and switch 22F in position L. The opening of gate 2116 applies an input to gate 207G so that an impulse on 21ft due to transition of switch 21F drives switch 23F to position 3.

Similarly a late transition occurring when 23F is in position 1 drives it into position 2 by the opening of gates 212G and 209G.

If switch 23F has been driven into position 6 by two late transitions, an early transition drives it back to position 5 by means of gates 2136 and 202G, whilst an early transition when switch 23F is in position 7 drives it back to position 6 by means of gates 2146 and 2046.

During the-initial period, whilst five marks and two spaces are being received, each transition from mark to space starts counter 11C from 102 milliseconds 1n its cycle as described above.

At milliseconds in the cycle, switch 12F is driven into position 2. At 80 milliseconds, counter 12C is given a step by application of potentials over gate 115G to open that gate, followed by the opening of gate 116G. Counter 12C is thus stepped into position 1. With counter 12C in position 1, potential applied from the counter 11C at 100 milliseconds in the cycle to gate 106G opens that gate, which causes opening of gate 1076 to cause element SP of switch 11F to be operated.

The stepping of counter 11C ceases, but is immediately resumed by the opening of gate 1056 to re-energise element ST of switch 11F. Any changeover of switch 11F results in an output 11ft being applied to the 0 stage of counter 12C and it restores counter 12C to position 0 and also applies an input to each of the gates 1026 and 1106. Which of these gates is opened depends upon the condition of switch 23F.

During the initial period above mentioned, the transit from space to mark, which should nominally occur at 0 milliseconds, is late in arriving in relation to the time scale, because the latter was started 2 milliseconds in advance of its normal time. The late occurrence of this transition drives switch 23F into position and therefore gate 102G is opened when switch 11F changes over and the counter 110 is reset at 102 milliseconds. Thus when element ST of switch 11F is re-operated and counter 11C starts stepping, it starts again from the 102 millisecond position. At 105 milliseconds switch 23F is restored to the position in which element 4 is conducting.

A similar sequence of events takes place when signal characters are sent. In such characters each transition from mark to space or space to mark will operate switch 23F to one position or another according to whether it is early or late and the counter 11C will be reset to 102 milliseconds if transitions are late and to 98 milliseconds over gate G if transitions are early.

If the counter 11C has been restarted from the 98 millisecond position, the switch 11F is unaffected when the counter reaches 100 milliseconds immediately thereafter, because the initial switch-over of switch 11F causes output 11ft to restore counter 12C; to position 0 and thus gate 106G will not be opened at 100 milliseconds.

Thus any lack of synchronism between the time scale circuit at the transmitter and the time scale circuit 11C is corrected periodically by reseting time scale circuit 11C forward or back from the position reached.

It will be appreciated that the resetting of time scale 110 can be varied by resetting it to different positions less than 100 milliseconds according to the number of early transitions i.e. according as 23F is in position 3, 2 or 1 and to different positions beyond 100 milliseconds according as 23F is in position 4, 5, 6, or 7. The time scale circuit 11C could be initially started at the 100 millisecond position and reset to that position if switch 23F remains in position 4.-

It will also be appreciated that the times at which switch 22F is changed over may be varied so that transitions are disregarded unless they occur within a small margin, say 3 milliseconds, either side of the nominal change-over time.

The receiving equipment can come to rest when transmission terminates. This condition can be recognised by the fact that a certain maximum number of characters arrive with elements entirely marks. The switch 13F is restored to position M at time 0 on the time scale of 11C. By means of a gate 1116 the condition of the switch 21F and thereby the condition of the incoming signals is examined at times 10, 30, 50, 70, 90, 110 and milliseconds in the time scale of 11C, i.e. one for each signal element and if a space is being received at any of these times switch 13F is driven to position S. If no space has been received so that switch 13F remains in position M, inputs are supplied to a gate 11126 at milliseconds in the time scale 11C to allow a pulse from a source of pulses P through the gate to step the counter 13C one step.

Thus the ten point counter 13C having positions 0 9 is stepped once for each character consisting wholly of marks. If nine such characters are received in succession, counter 13C reaches position 9, "but these must be nine consecutive characters, since each time switch 13F goes into positions S since its output 13 3 restores counter 13C to zero position over gate 113G. Counter 13C in position 9 drives switch 12F into position 1. Also in this position a potential is applied from 13c9 over gate 1086 and a second input is supplied from 1271. Gate 108G is opened, followed by the opening of gate 1076 and switch 11F is driven to position SP. With switch 11F in this position and counter 13C in position 9 a gate 1146 is opened and potentials applied over gate 113G to restore co unter 13C to position 0.

The receiving circuits then await the receiving channel going to space before restarting operations.

While the principles of the invention have been described above in connection with specific embodiments, and particular modifications thereof, it s to be clearly understood that this description is made only by way of example and not as a limitation on the scope of the invention.

What we claim is:

1. Telegraph receiver for receiving incoming signals consisting of equal length combinations of elements of two signalling conditions, said receiver comprising a time scale circuit and a pulse source for operating said time scale circuit to generate time position potentials, means for comparing the said potentials with the condition of incoming signals, and means controlled by the said comparing means for correcting the said time scale circuit in accordance with the positions in said time scale at which transitions from one signalling condition to the other occur.

2. Telegraph receiver for equal length combinations of elements of two signalling conditions comprising a source of regularly repeated pulses, a time scale circuit driven by said pulses, means for deriving from said time scale circuit potentials for examining the condition of incoming signals at predetermined positions in said time scale, means for regenerating signals dependent upon said condition at said predetermined positions, means for recording whether transitions from one incoming signalling condition to another occur early or late in respect of their nominal positions on said time scale, means for momentarily stopping and restarting said time scale circuit independently of the transmitter and of received signals, and means for adjusting the position in the time scale at which the time scale circuit is restarted under control of said recording means.

3. Telegraph receiver as claimed in claim 2 in which means is provided for restarting said time scale circuit from a position advanced or retarded from the position in which it was momentarily stopped according to whether said transitions have arrived during a portion of the time scale cycle late or early relative to the expected times.

4. Telegraph receiver as claimed in claim 2 in which said time scale circuit is composed of a series of static electric switches for counting pulses from a source of regularly repeated pulses.

5. Telegraph receiver as claimed in claim 2 comprising a first static electric switch, means for operating said switch from a first condition to a second condition and from said second condition to said first condition upon said time scale circuit reaching positions in predetermined relation to the nominal positions at which said transitions may be expected, a second static electric switch, means for operating said second switch into one condition or the other in dependence 'upon incoming signals, and means for producing a momentary pulse at each change of condition of said second switch, the said means for recording being dependent upon the condition of said first switch when said pulse occurs.

References Cited in the file of this patent UNITED STATES PATENTS 2,527,638 Kreer Oct. 31, 1950 2,749,386 Wright June 5, 1956 2,752,425 Dain June 26, 1956 2,816,163 Robin Dec. 10, 1957 2,822,422 Terry et al Feb. 4, 1958 FOREIGN PATENTS 148,166 Australia Sept. 11, 1952 148,467 Australia Sept. 30, 1952 

